The present disclosure relates to a semiconductor device, and relates, for example, to an associative memory.
The storage device called an associative memory or a CAM (Content Addressable Memory) searches for a matching search word from stored data words, and, when a matching data word has been found, outputs its address.
The CAM includes BCAMs (Binary CAM) and TCAMs (Ternary CAM). Each memory cell of the BCAM stores information “0” or “1”. In the TACM, each memory cell can store information not only “0” and “1”, but also “Don't Care” (in this example, a symbol “*” is used). The symbol “*” represents that any of “0” and “1” is possible.
The TCAM device is widely used for address search and access control of a router for network, such as the Internet. To deal with the large memory capacity, the TCAM device generally has a configuration with a plurality of arrays and for executing search operations simultaneously for the arrays.
The TCAM device can compare input search data (input packet) and TCAM cell data at once. Thus, it can perform the entire searches at a higher speed than the RAM (Random Access Memory). However, a problem is that the consumption power is increased due to generation of a search current at the time of the search.
For this point, when a non-matching result (MISS) is generated based on searching (pre-searching) of the initial-stage segment by a time division search, it is possible to attain low power consumption for the search by not executing searching (post-searching) of the post-stage segment (Japanese Unexamined Patent Application Publication No. Sho 62-293596).